Electrode Polarity - which info. is correct

Talking stick welding here and electrode polarity. Everything I've read has said with electrode +ve you get max. penetration, and with electrode negative you get less penetration.

I've got a book from Hare & Forbes - Metal Fabrication Course - Apprentice Reference Notes (the thick green A4 paperback with pages that look like terrible photocopies). On page 331 it says the following:

"When a welding current flows across an arc gap 2/3 of the heat of the arc is generated on the side (pole) which is being bombarded by the electrons".

Then a bit further down:

"......the greater amount of heat can be concentrated on the parent metal to increase to increase the depth of penetration, by making the parent metal positive and the electrode negative. Alternatively if greater deposition rate is important the parent metal should be connected negative and the electrode positive, the greater amount of heat increasing burn off rate".

This is completely opposite to what I have "learned" so far. Which one is wrong ?? I've tried electrode negative and thought it made the rod a bit more aggressive, as has another member here who said it made his burn through issue worse. Now I'm left scratching my head about this one.

Cheers,

Keith.

Just found an answer from another forum. It seems the book is right but only for bare metal electrodes, which means it's wrong when applied to stick welding electrodes. Here's the answer:

This can be a confusing issue to a lot of people. "Welder" is 100% correct from a strictly electrophysics standpoint. DCEN puts more of the heat into the work and DCEP concentrates the heat onto the electrode. The problem arises in the fact that this only holds true if you are using GTAW or are stick welding with a bare electrode. It does not take into account that penetration is greatly influenced by the plasma gases created by different flux coatings. Markopolo and DDA52 are correct about 95% of the time when they state that in SMAW, DCEP gives deeper penetration. You always have to go by what the manufacturer says concerning the use and characteristics of a particular electrode. Most reverse polarity rods are designed to have the metal core melt faster that the flux coating. This forms a cup like crater at the end of the electrode and the theory is that the molten metal and positive ions created in the arc plasma shoot across the arc with such force and attraction for the negatively charged workpiece that this is what causes you to get a more aggresive arc and deeper penetration. Again, it depends on the flux coating, but most of the time in SMAW, reverse polarity will give you deeper penetration. If you are TIG welding, then you will want to go with "Welder", and get your deeper penetration with DCEN. By the way, it is that same bombardment of positively charged ions in the plasma, being attracted to the negativlely charged work, that breaks up the oxides when using AC GTAW to weld aluminum.

There's a few threads on this forum regarding this topic which are worth reading and highlight the difference of opinions on this. My take on it is:

• as electrons jump from the -ve electrode (which would be the rod if you are using stick DCEN) across the arc gap to the +ve side (the work piece in this case), the "evaporation" of electrons from the -ve electrode will cool the rod, whilst the "condensation" of the electrons on the work will make that end of the arc relatively hotter. This is easy to verify with TIG welding. Similarly, you would think that DCEN in stick welding would result in far more penetration as the work piece is receiving about 2/3 of the heat, with only 1/3 on the rod. However...
• If you change the polarity to DCEP, even though the electrons are now running the other way and the rod is in theory getting 2/3 of the heat, this heat is rapidly being transferred back to the work piece in the form of molten drops of metal being deposited into the weld pool.
• So in terms of penetration with stick welding it is not straight forward, as most of the heat ends up in the weld pool anyway irrespective of whether it was generated at the tip of the rod on on the work piece.
• This is where the flux composition, etc. come in... the "aggressiveness" you note with DCEN could well be the relative difference in flux burn off rates compared to exposure of the metal at the tip of the rod and hence difference arc characteristics.

SAW - DCEP & DCEN deposition rate has a pretty technical discussion if you're that way inclined.

Personally, with 6012/6013 electrodes (sorry, can't remember the AS codes) I find DCEP generally nicer (gentler?) to weld with, but I have noticed that DCEN gives a slightly smoother weld bead. I've given up trying to understand why.

Cheers

- Mick

Quote:

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Originally Posted by WelderMick

I've given up trying to understand why.

Cheers

- Mick

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Thanks very much Mick. I think in thise case that's the best way to go. We've got enought to learn and do without getting into the sub-atomic physics of why. I've always been a bit of a bookworm but feel I need several life times to learn everything I'd like to.

My main concern was that everything I'd read and been told may have been untrue. I now see that it's generally true but there are variables based on individual rods and their flux coatings.

Keith.

not too sure about all the electrons and stuff boys, but i know that when i gouge with the arc air all day, i run electrode positive, and just looking at the way the metal blows away and the carbon doesn't, the 2/3's of heat would be in the work, yeah? when you see a bloke try to gouge electrode negative, the carbon sticks and glows orange/white almost instantly.....hmmm.

Like Mick I've also given up. I started with DCEN, was advised to try DCEP for some reason, liked it and went with it for a while. However, recently I've moved back to DCEN. Again, not sure why (maybe the rods I've been using - someone advised they produce a nicer bead with DCEN? Maybe?).

For me, both work fine with the home jobs I do. As long as I have some idea of appropriate current range and particular rod characteristics for a given polarity I can produce a reasonable result.

Yep, there's plenty of welders who swear by DCEP or DCEN and claim the other polarity is disastrous, usually giving some half-baked explanation as to why their preferred polarity is correct, simultaneously showing why they are welders and not physicists. Both, depending who you speak to, give better penetration, both burn the stick faster, both put more heat in the work, both give both less and more blowthrough, both are better for thin sections - the list goes on.

Me? I can barely tell the difference.

Selection of an electrode polarity is, but a single parameter of what goes into performing a weld bead suitable for its intended purpose.

Ok ! Its one just element, not the whole shebang.
If the other parameters like

• Arc length
• Travel speed
• Angle of incline
• Amperage
• Correct electrode diameter to material thickness
• Correct electrode type selection

which have a greater impact upon a suitable welded deposit.

They are not called the basics for nothing!

What is correct?. Whatever gives the the best for your current situation is correct.

The point is missed severely when people welding on every day non critical strength jobs, waffle on a about depth of penetration relative to polarity.

How they observe, measure or define a deeper penetration of one polarity of one over the other is a mystery to me? I for one, won't feel too insecure if I know I have welded the garden gate with a polarity other that what is recommended by the book. The quest for improvement is to be commended, but place the effort where it will yield the best result.


Grahame

Just a word of thanks to everyone, it's really cleared up a few things about this polarity issue. As a relative beginner, and trying to find whatever info I can, it gets frustrating when you try and apply some of the theory which I've read in various places, and it just didn't seem to work that way.

Then you guys tell of your real world experience and the theory started getting turned on it's head a bit. It never fails to amaze me what practical, real life info gets left out of teaching materials.

Keith.